Generative manufacturing methods are used by their iterative joining of layer elements or volume elements onto or to one another in order to produce three-dimensional objects, and their application is found in the region of the production of prototypes as well as recently also in component production, particularly for the fabrication of individually shaped components. A multiplicity of different materials are available as starting materials, which may be in powder or granules form, but also in the form of liquids, for example as suspensions. In generative production methods, the three-dimensional object is formed by a multiplicity of individual material layers, which are deposited successively on a lowerable component platform and are subsequently subjected individually to a locally selective solidification process.
In order to make a component by means of selective laser (beam) melting (SLM), a powder bed is irradiated by means of a laser beam according to a predetermined irradiation file, in which the data are generated from a 3D CAD file. In the calculation step, the component is subdivided into individual layers. In the second calculation step, the paths (vectors) along which the laser beam travels are generated for each layer.
Once a powder layer has been irradiated, the component platform is lowered and a new layer of powder is applied by means of a spreader, for example a rake, and then irradiated again with the laser and with the aid of the irradiation file. This is continued until a component has been fully generated. Especially with selective laser beam melting, it is possible to generatively construct components with complex hollow structures.
The surface roughness is determined in this process (normally 20 μm-40 μm) by the method parameters (laser power, beam diameter, movement speed) as well as the particle size fraction of the powder material used. Furthermore, the intensity profile of a laser beam has an intensity distribution which can be described by a bell-shaped profile (Gaussian distribution). This means that the intensity maximum lies at the center of the laser beam and the intensity decreases toward the edges of the laser beam. Because of this, during melting of the powder bed, a temperature maximum is reached on the surface of the powder bed in the middle of the laser beam, the temperature decreasing toward the edge and not being sufficient to melt the particles at the edge. Because of this, in particular, problems are incurred on the surface of the powder bed at the edge of the component cross section to be produced. This is because the laser beam must remain at the edge of the cross section until the edge particles of the component to be produced have been melted. In the vicinity of the edge, namely where the intensity maximum of the laser beam lies, an excessively high amount of energy has however already been delivered at this time. The process is therefore difficult to control, in particular at the edge of the cross section. This gives rise to relatively large averaged roughness depth values Rz (average value of the measured roughness depths) or average roughness values Ra (arithmetic mean of the deviations from the midline). Internally lying surfaces can therefore be reprocessed poorly or not at all after the selective laser melting process.